This invention relates to a process for the surface treatment of aluminum and alloys thereof to improve the corrosion resistance and adhesion of paints to the surface.
In conventional surface treatments of aluminum and its alloys, there have been generally employed metallic compounds of, for example, chromium, iron, manganese, aluminum, zinc, nickel, calcium and the like as water-soluble inorganic compounds together with phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, chromic acid, boric acid and the like to deposit water-insoluble salts on the metal surface to improve the corrosion resistance and adhesion of paints applied thereto. These have been generally employed as aqueous chemical conversion coating solutions. Chemical conversion coatings containing predominantly metallic compounds other than the above-listed ones may provide insufficient corrosion resistance and adhesion of paints applied thereon. Moreover, the use of treating liquid compositions containing heavy metal ions, such as chromium, is restricted because of environmental discharge limitations.